1. Field of the Invention
This invention resides in the field of cell sorting, i.e., the selection of biological cells having particular characteristics of interest from cell populations that include both these cells and others that do not possess the characteristics of interest.
2. Description of the Prior Art
The sorting of biological cells to select cells having particular characteristics from larger populations is a procedure frequently used in biological laboratories for genomic studies, stem cell studies, and cell-based screening. Sorting allows individual cells that possess a particular characteristic to be identified and isolated for purposes of counting, further study, removal, or treatment. Sorting is commonly performed by dispersing the entire population of cells in a liquid carrier to form a suspension and then analyzing the suspension by flow cytometry to detect and either separate or individually treat the cells of interest. This method is not suitable for adherent cells, however, which are the most common phenotype of biological cells. Adherent cells can be made non-adherent, i.e., detached from the surfaces on which they are grown or from other cells to which they adhere, by enzymatic or mechanical means, but detachment is detrimental to cell health and alters the morphology of the cells and the intracellular processes that are associated with the morphology. Detachment also obliterates various traceable markers on the cell surfaces such as filopodia and localized membrane proteins which often contain the characteristics that are the reasons for the sorting.
One method for analyzing adherent cells without loss of these characteristic features is by plating the cells on a growth surface where they can be identified through a microscope. Such visual identification is tedious and prone to error, however, and robotic systems that utilize machine vision have therefore been used for greater accuracy. Whether sorting is done visually or by machine, however, complexities are involved such as the use of sacrificial base layers, the excising of sections of the surface on which the cells of interest reside, or the use of micropallets for localized plating of individual cell types.